Photosynthesis: Seasonal shift

Science 351, 696–699 (2016)

The seasonal cycle of atmospheric CO₂ concentrations has grown more pronounced in the northern high latitudes over the past five decades, indicative of large-scale changes in terrestrial carbon fluxes. Model simulations suggest that an increase in plant carbon uptake is responsible.

Matthias Forkel, of the Max Planck Institute for Biogeochemistry, Germany, and colleagues use a global vegetation model, trained with satellite data, to assess the extent to which changes in vegetation dynamics can explain the latitude-dependent amplification of the seasonal CO₂ cycle. They find that an increase in net biome productivity, primarily in boreal and arctic ecosystems and underpinned by an increase in gross primary production, contributed significantly to the trend. The amplification disappeared in simulations in which climate or vegetation cover was held constant, suggesting that climate change and the shift from herbaceous vegetation to forests caused the increase in photosynthetic carbon uptake, and thus the amplification of the seasonal cycle, in northerly latitudes.

The researchers note that the climate-driven increase in plant productivity in the northern high latitudes is likely to subside at some point, due to resource and other limitations.